Two Phase Water Jet Propulsion for High-Speed Vehicles

ABSTRACT

A water jet propulsion apparatus having an engine producing an exhaust gas, a pump driven by the engine, a nozzle in fluid communication with the pump, and an exhaust passageway communicating between the engine and the nozzle is disclosed. The exhaust passageway is connected the nozzle at a point in the nozzle where the water flow velocity is being increased, and prior to the water being expanded. By mixing the exhaust with the water while the water flow velocity is being increased, the result is a decrease the density of the mixture and an increase the total mass flow rate, thus resulting in increased thrust.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefore.

CROSS REFERENCE TO OTHER PATENT APPLICATIONS

None.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a water propulsion apparatus, and moreparticularly to a two phase water jet propulsion apparatus.

(2) Description of the Prior Art

In a typical water propulsion system, the system employs a pumpconnected to a nozzle. The pump, usually a high speed centrifugal waterpump, is driven by an engine such as a two stroke gasoline engine, fourstroke gasoline engine, or a diesel engine. The system produces thrustby first increasing velocity of the water flow, and subsequentlyexpanding the water flow.

The engine used to pump the water in the water propulsion systemgenerates exhaust gas and sound waves. The exhaust and sound waves aredirected away from the engine compartment by an exhaust system orpassageway that is connected to an exhaust port of the engine. Theexhaust system is then either extended to open into the water or intothe air/atmosphere. In the exhaust systems where the exhaust gas isdischarged into the atmosphere, the exhaust noise creates a problem.

In the propulsion systems where the exhaust is introduced into thewater, the exhaust is introduced in a low-pressure region or after thewater begins to expand. While introducing the exhaust gas into thelow-pressure region (after the water has expanded) reduces the soundswaves (noise level), this does not increase the efficiency of the waterpropulsion system or increase thrust of the water propulsion system.

Accordingly, a need exists for a water propulsion apparatus that reducesthe noise level generated by the engine. The apparatus should alsoincrease the thrust produced by the propulsion apparatus. Moreover, theapparatus should increase the overall efficiency of the propulsionapparatus.

SUMMARY OF THE INVENTION

A water propulsion apparatus is disclosed which includes a nozzle and apassageway communicating with an exhaust gas source. The nozzle includesa first region that increases the water flow velocity and a secondregion that subsequently expands the water, thereby producing a thrust.The passageway is connected to the nozzle at a point in the first nozzleregion while the water flow velocity is being increased and prior to thesecond nozzle region wherein the water being expanded. In a preferredembodiment, the exhaust gas source is an engine. The engine can be adiesel engine, a gasoline engine, or a hot gas piston expander.

In a further embodiment, the present invention includes a method ofincreasing the thrust of a water propulsion apparatus. The methodincludes the steps of providing an engine that produces an exhaust gas,providing a nozzle having a first region which increases the water flowvelocity and a second region which subsequently expands the water, andintroducing the exhaust gas at a point in the first nozzle region whilethe water flow velocity is being increased and prior to the secondnozzle region wherein the water is being expanded.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood in view of the following description of the inventiontaken together with the drawing wherein:

FIG. 1 is a schematic view of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a water propulsion apparatus 10 in accordancewith the present invention, generally includes an exhaust gas source 12,a nozzle 14 and a gas passageway 15. The exhaust gas source 12 ispreferably an engine, though other gas producing sources would berecognizable to those skilled in the art. In a preferred embodiment, theengine is a diesel engine, a hot gas piston expander or a gasolineengine but not limited to, a two stroke engine or a four stroke engine.

The engine 12 drives a pump 16, typically a high-speed centrifugal pump,via a drive means 17 (such as, but not limited to, a drive shaft,transmission, drive belt, etc.) that displaces water through a waterintake 18 from a water source (not shown), through the pump 16, and intothe nozzle 14. As the speed of the pump 16 is increased, the amount ofwater displaced, the mass flow rate “M”, is increased. For a given pumpspeed, the pump 16 will substantially have a constant mass flow rate M.

The nozzle 14 is fluidly connected to the pump 16, and can be any nozzleknown to those skilled in the art. In general, the nozzle 14 is aconverging passageway wherein the nozzle diameter at region R₁ is largerthan the nozzle diameter at region R₂. For a given mass flow rate M, thedecrease in the diameter from R₁ to R₂ increases a velocity “V” of thewater, and consequently increases the momentum of the water. As theaccelerated water exits the nozzle 14 at a nozzle outlet 20, theincreased momentum translates into thrust. The thrust produced by thenozzle 14 is approximated by the difference in the momentum of the waterjet:

Thrust=MV _(Jet) −MV   (1)

where M is the mass flow rate through the system, V is the velocity ofthe vehicle, and V_(Jet) is the velocity at the nozzle which isnominally:

V _(Jet)=(2(P _(Pump) −P _(Ocean))/ρ_(Ocean))^(1/2)   (2)

where P_(Pump) is pressure of the pump, P_(Ocean) is the pressure of theocean, and ρ_(Ocean) is the density of the water. This principle is wellunderstood and known by those skilled in the art.

A result of decreasing the diameter of the passageway, and consequentlyincreasing the water velocity, is that the pressure within the nozzle 14at region R₁ is greater than the pressure at region R₂. This effect isreflected by Bernoulli's Equation.

In the past, most engines operate efficiently at lower exhaustback-pressures. Exhaust back-pressure is a measurement of the resistanceto the flow of exhaust encountered by the engine. By and large, asengine exhaust back-pressure increases, the engine 12 requires morepower to remove the exhaust gasses 15 from a combustion chamber of theengine, thus reducing the performance and efficiency. New enginedesigns, however, actually operate more efficiently at higher Net MeanEffective Pressure (NMEP). NMEP can be derived/defined from anexpander's or engine's net power, shaft speed, and volume displaced, andis approximated by:

$\begin{matrix}{{NMEP} = \frac{{NET}\mspace{14mu} {POWER} \times {RPC}}{{VD} \times {RPM}}} & (3)\end{matrix}$

The variable “RPC” (output shaft revolutions per cycle) is one for hotgas piston expanders, one for a two stroke internal combustion engine,and two for a four stroke internal combustion engine. Table 1 summarizesthe maximum power for several engines.

TABLE 1 Rated ENGINE Rated Power Speed Displacment RPC NMEP Merc. 2.4Litre 240 hp 7000 rpm 142 in³ 1  96 psi GM 5.7 Litre 210 hp 4400 rpm 350in³ 2 108 psi DD 6V053TA* 350 hp 2800 rpm 305 in³ 1 162 psi Cummins 370B370 hp 3000 rpm 379 in³ 2 257 psi *Detroit Diesel

A gas passageway 22, according to the present invention, is connected tothe nozzle 14 at a region R₃ where the velocity of the water flow isbeing increased, yet prior to the water being expanded. This region R₃is in a high-pressure region of the nozzle 14. The resulting thrust canbe approximated by:

Thrust=(M+M _(Exhaust))V _(N) −MV   (4)

where:

V _(N)=(2(P _(Pump) −P _(Ocean))/ρ_(Mixture))^(1/2)   (5)

This results in the exhaust 15 being mixed with water in the nozzle 14.Consequently, the density, ρ_(Mixture), is decreased, the total massflow rate, (M+M_(Exhaust)), is increased, and the thrust is increased.When the water propulsion apparatus 10 is used in combination with theengine (gas source) 12 which operates most efficiently at an increasedNMEP, the result is a water propulsion apparatus having increasedthrust, increased efficiency, and decreased noise levels.

The water propulsion apparatus 10 may be used in on personal watercraft(or “Jet Ski”) or high speed underwater vehicles (such as torpedoes) orhigh speed surface craft.

It will be understood that many additional changes in the details,materials, steps and arrangement of parts, which have been hereindescribed and illustrated in order to explain the nature of theinvention, may be made by those skilled in the art within the principleand scope of the invention as expressed in the appended claims.

1. An apparatus for water propulsion, said apparatus comprising: a pumpcapable of pumping from a water source; a nozzle in fluid communicationwith said pump, said nozzle including a first region capable ofincreasing a velocity of a water flow by a decreasing diameter of thenozzle and second region adjacent to and converging in diameter fromsaid first region with said second region capable of producing a thrustbased on the velocity of the water flow; and a passageway communicatingwith an exhaust gas source and at a single point as an only point ofpassageway communication in said first region of said nozzle and priorto said second nozzle region such that the thrust is increasable byexhaust gas impacting the water flow.
 2. The apparatus in accordancewith claim 1 wherein said exhaust gas source is an engine.
 3. (canceled)4. (canceled)
 5. A device for water propulsion, said device comprising:a nozzle in fluid communication with a pump, said nozzle including afirst region capable of being set to a first pressure and a secondregion adjacent to and converging in diameter from said first region,said second region capable of being set to a second pressure, whereinthe first pressure is greater than the second pressure; and a passagewaycommunicating with a source of exhaust gas and at a single point as anonly point of passageway communication within said first region of saidnozzle, wherein said exhaust gas is combined with water in said firstregion to increase a thrust of the water propulsion based on a waterflow within the nozzle.
 6. A method of increasing a thrust of a waterpropulsion apparatus, said method comprising the steps of: providing apump; producing an exhaust gas; driving said pump; providing a nozzle influid communication with said pump, said nozzle having a first regioncapable of increasing a velocity of flow of water and a second regionadjacent to and converging in diameter from the first region, the secondregion capable of expanding the flow of water; introducing the exhaustgas at a single point as an only point of the exhaust gas introductionin the first nozzle region while the velocity is being increased andprior to the second nozzle region wherein the water is being expanded;and increasing a thrust by an increase in velocity resulting from theexhaust gas introduced at the point in the first nozzle.